ES2701315T3 - Encapsulation procedure of polycarbonate glazing provided with an anti-scratch coating - Google Patents

Abstract

Method of encapsulating a polycarbonate glazing comprising, at least in some of its faces, a hard silicone-based anti-abrasion coating, said process comprising the following successive steps: a) treating a region of the glazing face carrying the coating hard based on atmospheric plasma silicone with a plasma nozzle having a power between 100 volts and 1,000 volts, the distance between the end of the plasma nozzle and the glazing surface being a maximum equal to 7 mm, b) applying, on said region treated by atmospheric plasma, a primer composition comprising one or more adhesion promoters selected from the chlorinated diisocyanates, polyisocyanates and polyolefins, in solution or suspension in an organic or aqueous solvent, c) evaporating the solvent to form a layer of dry primer, and d) overmold a thermoplastic polymer static over the region covered by the dry primer layer.

Description

DESCRIPTION

Encapsulation procedure of polycarbonate glazing provided with an anti-scratch coating

The present invention relates to a novel method for encapsulating glazings of motor vehicles made of polycarbonate comprising a step of atmospheric plasma pretreatment.

In the industrial field of motor vehicle glazing, the term "encapsulation" denotes a method or step of overmolding a polymeric material around the perimeter of a glazing. The material is injected in a fluid state in a mold that forms a watertight frame around the edge of the glazing. After hardening the material by a polymerization and / or crosslinking reaction (in the case of thermosetting polymers) or by cooling (in the case of thermoplastic polymers), the mold is opened and removed, leaving on the periphery of the glazing a profiled bead in contact with the edge and at least one of the two faces of the glazing, often with both sides of the glazing.

The polymer that forms the profiled cord is often an elastomer capable of acting as a joint between the glazing and the body. Polymers that are not elastomers, however, can also be overmolded by encapsulation in order to perform other functions. The profiled cord obtained is then generally a composite cord that simultaneously comprises elastomeric elements and non-elastomeric elements juxtaposed.

The encapsulation step is generally preceded by a step of cleaning and activating the surface to be overmoulded, on the periphery of the glazing, then a primer is applied on the activated region intended to come into contact with the overmolded profiled cord.

In the field of glazing of motor vehicles made of mineral glass, the use of plasma activation at atmospheric pressure, also called cold plasma, is known. The oxidation of the surface results in the formation of reactive groups, predominantly SiOH groups, capable of reacting with the primer.

In the field of glazing of motor vehicles made of polycarbonate, this technique of activation by plasma, before priming and encapsulation, has not yet allowed to obtain satisfactory results.

Polycarbonate is a material used as a replacement for silicate glass for certain glazings such as glazed ceilings, fixed side windows and rear windows, and also for the diffuser glass of the headlights. Despite numerous advantages (low weight, impact resistance, ease of molding) polycarbonate suffers, as a replacement material for motor vehicle glass, a high sensitivity to chafing.

All glazings of polycarbonate motor vehicles, therefore, must be covered with a hardcoat ( scratch resistant ) and scratch resistant ( anti-scoring) to ensure sufficient transparency of the glazing throughout. of the whole life of the vehicle.

These coatings are nanocomposites based on silicone (polyorganosiloxanes) and nanoparticles with a high hardness, generally silica particles. They are hydrophobic coatings having a surface energy of less than 30 mN / m and a thickness of the order of several hundred nanometers (100-1,000 nm).

When it is desired to encapsulate polycarbonate glazing protected by such anti-scratch / anti-scratch coatings, commonly denoted by the English term hardcoat, the difficult problem of activating this very hard, chemically inert and difficult to wet surface is faced. The treatment known for atmospheric plasma used successfully for mineral glass does not allow the activation of the surfaces of the hard coatings covering the polycarbonate glazing.

Nor is any satisfactory chemical treatment known to improve the surface wettability of hard silicone coatings, increase their roughness and introduce chemical functions capable of reacting with the components of the primer (isocyanates).

Heretofore, the only satisfactory technique that makes it possible to obtain a good adhesion of the primer compositions and the injected encapsulation materials is the removal of the hard coating by mechanical abrasion of the surfaces to be encapsulated. This technique, however, has a number of problems:

- Fine dust of plastic materials can be inhaled by nearby operators;

- mechanical abrasion prolongs the cycle time and imposes great limitations for the design of the production area (closed chamber, extraction system);

- dust generated by mechanical abrasion can deposit in plastic glazings and create unacceptable defects after encapsulation;

- Many preventive cleaning operations are necessary.

Within the context of his research with the objective of replacing the mechanical abrasion of hard coatings on polycarbonates, the Applicant has noted with surprise that a known technique, hitherto judged inefficient, has allowed this objective to be achieved with the condition that it be used in unusual conditions.

The atmospheric plasma technique is effectively used industrially with nozzle / substrate distances to be activated between approximately 1 and 5 cm depending on the material to be treated, the power of the plasma, the size of the nozzle and of the displacement speed. By performing cold plasma activation tests with much smaller nozzle / substrate distances, the inventor realized that this known technique made it possible, contrary to what had been observed to date, to increase the surface energy and the roughness of the treated regions and introducing into them, especially by oxidation, chemical functions capable of reacting with the primer compositions.

Contrary to what had been feared, this abrasion by "near" cold plasma does not produce any thermal degradation of the treated glazings. It also makes it possible to shorten the cycle time and considerably reduce the costs associated with encapsulation. The absence of dust formation is a considerable advantage from the point of view of the environment and the health of operators.

To obtain satisfactory adhesion results between a polycarbonate glazing and an overmolding bead made of thermoplastic polymer (whose hardening in the encapsulation mold does not involve a chemical reaction) it has further been necessary to carry out a priming of the plasma treated region. Certain primers have proven to be particularly satisfactory from this point of view.

The object of the present invention is a method for encapsulating a polycarbonate glazing comprising, on at least one of its faces, a hard silicone-based anti-abrasion coating, said method comprising the following successive steps:

a) treating a region of the face of the glazing that carries the silicone-based hard coating by atmospheric plasma with a plasma nozzle having a power preferably comprised between 100 volt-amperes and 1,000 volt-amperes, the distance between the nozzle end being Plasma and the surface of the glazing at most equal to 7 mm,

b) applying, on said region treated by atmospheric plasma, a primer composition comprising one or more adhesion promoters selected from the diisocyanates, polyisocyanates and chlorinated polyolefins, in solution or suspension in an organic or aqueous solvent.

c) evaporate the solvent to form a dry primer layer, and

d) overmolding a thermoplastic polymer over the region covered by the dry primer layer.

In the present application, the terms plasma nozzle and plasma torch are used interchangeably to denote a plasma source that generates a post-discharge out of thermal equilibrium.

By "distance between the end of the plasma nozzle and the surface of the glazing" is meant the shortest distance between the exit orifice of the plasma jet and the surface of the hard coating to be treated.

The plasma nozzle preferably has a power comprised between 200 and 900 volt-amperes, in particular between 300 and 800 volt-amperes, and ideally between 400 and 700 volt-amperes.

The plasma nozzle may be a rotating nozzle in which the outlet orifice of the plasma jet rotates at a high velocity on the central axis of the nozzle. In such a rotary nozzle, the axis of the plasma jet may be normal to the surface to be treated, but may also be tilted relative to this normal. The angle of the cone formed by an inclined jet of a rotating nozzle is generally between 10 and 30 °, in particular between 12 and 20 °. The axis of the plasma jet is preferably inclined towards the outside, which has the effect of increasing the treated region.

Such rotating plasma nozzles are sold, for example, under the name of Openair® by the company Plasmatreat.

The rotating nozzles have the advantage of allowing the treatment of relatively wide regions at the edge of the glazing. The width of the strip that can be treated in a single pass of the nozzle is roughly equal to the diameter of the rotation circle of the nozzle orifice.

Preferably, rotating nozzles will be used to treat, in a single pass, a band having a width comprised between 1 and 5 cm, preferably between 1.5 and 4 cm and particularly preferably between 2 and 3 cm.

The distance between the end of the plasma nozzle and the surface of the glazing is preferably less than 6 mm, in particular at most equal to 5 mm, and ideally between 2 mm and 4 mm.

In step (a) of the method according to the invention, the plasma torch moves with respect to the glazing which is going to be treated. This displacement can be created by means of a moving torch and a fixed substrate or also by means of a fixed torch and a moving substrate that moves in front of this fixed torch, the latter embodiment being preferred.

The relative displacement speed of the plasma nozzle with respect to the glazing is preferably between 1 and 5 m / minute, in particular between 2 and 4 m / minute. Between these margins, it will generally be used a relative displacement speed the greater the smaller the distance between the end of the nozzle and the substrate to be treated.

The plasma nozzle typically operates with a carrier gas pressure comprised between 3 and 4 bar. Preferably the carrier gas is filtered air.

The process of the present invention in principle comprises embodiments in which the plasma torch passes several times over the same region of the substrate to be treated. When this is the case, the nozzle distance and the travel speed may be identical for all passes. One and / or the other may however be different from one pass to another. When step (a) of the method comprises several passes of the torch over the same region of the substrate, it is essential that at least one pass be carried out under the conditions defined in the independent claim. The one or the other passes could be carried out in other conditions, in particular at a greater nozzle-substrate distance.

Preferably, step (a) does not comprise more than a single pass of the plasma nozzle on each point of the glazing to be treated.

The cold plasma treatment (step (a)) increases the surface energy and, therefore, the wettability of the silicone-based hard coating. Prior to treatment, this surface energy is less than 30 m N irr1.

After the plasma treatment step according to the invention, it is at least 45 m N irr1, preferably greater than 50 mN-irr1 and ideally greater than 60 m N irr1.

In a second step of the process according to the invention, a primer composition is applied on the plasma treated region.

This composition is a liquid composition containing one or more adhesion promoters in solution or in suspension in an organic or aqueous solvent.

The application can be carried out according to known application techniques, for example by means of a felt or a foam impregnated with the primer composition, or also by the application of an aerosol by means of a spray.

The thickness of the primer film before drying, preferably is less than 300 μm, in particular between 20 μm and 200 μm.

The drying can be carried out at room temperature or under a slight heating, preferably it is carried out at room temperature.

After the drying step, the dried primer layer formed on the plasma treated region generally has a thickness of less than 30 μm, in particular between 2 and 20 μm.

The adhesion promoter (s) are selected from the group consisting of diisocyanates, polyisocyanates and chlorinated polyolefins. The aliphatic diisocyanates or polyisocyanates allow a particularly effective priming.

The total content of diisocyanates and polyisocyanates of the primer composition is generally between 20 and 40% by weight, preferably between 25 and 38% by weight and in particular between 30 and 35% by weight.

The content of chlorinated polyolefins of the primer composition is generally between 5 and 25% by weight, preferably between 7 and 20% by weight and in particular between 10 and 15% by weight.

In a particularly advantageous embodiment, the adhesion promoters are selected from the group consisting of isophorone diisocyanate (IPDI), 4,4-diphenylmethane diisocyanate (MDI) and chlorinated polyolefin grafted with maleic anhydride.

The chlorinated polyolefins preferably have a chlorine content of between 5 and 20% by weight, preferably between 10 and 15% by weight, and their average weight by weight is preferably between 50,000 and 200,000, preferably between 80,000 and 120,000 .

These polyolefins are available on the market and are sold, for example, under the references Eastman Chlorinated Polyolefin (Eastman), Superchlon (Nippon Paper), and Hardlen (Toyobo).

After the evaporation of the solvent phase, the edge of the glazing, with the plasma-treated region (s) and cover (s) by the dry primer layer and surrounded by a mold and a thermoplastic polymer is injected in the molten state.

The thermoplastic polymer is selected, for example, from styrenic thermoplastic elastomers (TPE-S), vulcanized olefinic thermoplastic elastomers (TPE-V), poly (vinyl chloride), thermoplastic polyurethanes (TPU), poly (methacrylate) of methyl) (PMMA), polycarbonates (PC), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), polycarbonate / acrylonitrile-butadiene-styrene blends (PC / ABS) and polypropylene (PP).

Among these thermoplastic polymers, elastomers, in particular styrenic thermoplastic elastomers (TPE-S), vulcanized olefin elastomers (TPE-V), and plasticized polyvinyl chloride (PVC), will be preferably used.

The TPE-S that can be used in the present invention mainly comprise the following families:

SBS (styrene-butadiene-styrene): block copolymers comprising a central polybutadiene block flanked by two polystyrene blocks.

- SEBS (styrene-ethylene-butadiene-styrene): copolymers obtained by hydrogenation of SBS,

- SEPS (styrene-ethylene-propylene-styrene): copolymers comprising a central block of poly (ethylenepropylene) flanked by two blocks of polystyrene,

- SEEPS (styrene-ethylene-ethylene-propylene-styrene): copolymers obtained by hydrogenation of styrene-butadiene / isoprene-styrene copolymers.

These polymers are commercially available in grades that contain mineral fillers, but also in the form of materials without fillers.

In the present invention, use will be made of TPE's that are essentially free of fillers, or that contain less than 5% of mineral fillers, preferably less than 2% of mineral fillers.

They are available, for example, under the following trade names: Dryflex (Hexpol TPE), Evoprene (AlphaGary), Sofprene (SOFt Er), Laprene (SOFTER), Asaprene (Asahi Kasei) and Nilflex (Taroplast).

These products may contain a certain fraction of plasticizers, fluidifiers or organic lubricants.

The melting point of the TPE-S is advantageously between 180 ° C and 210 ° C, in particular between 190 ° C and 200 ° C.

In the molten state, they must be sufficiently liquid to be molded by injection. However, it is impossible to give precise indications regarding its viscosity in the molten state, since it depends not only on the temperature but also on the shear stress to which the polymers are subjected. The suppliers generally propose qualities called "for injection molding"

Vulcanized olefinic elastomers (TPE-V, or TPV according to ISO 18064) are mixtures of a thermoplastic polymer, generally polypropylene (PP), and a rubber, typically EPDM, crosslinked during extrusion manufacturing. Due to this vulcanization during extrusion, these polymers are also known as "dynamic vulcanizates" ( dynamic vulcanisates). The gummy phase is dispersed in the thermoplastic matrix.

As an example of commercially available TPE-V, the Sarlink® 4775B42 (Teknor Apex Co) can be cited.

Plasticized PVCs, or flexible PVCs, contain large amounts of plasticizers, typically between 40 and 60% by weight. Its melting point is between 160 and 200 ° C.

Mention may be made, as an example of plasticized PVCs advantageously used as encapsulating polymers, of the following commercially available products: BENVIC® (Solvay), TECHNIfAx® (Littleford Day), NAKAN® (Resinoplast) and SUNPRe Ne® (Mitsubishi).

Example

Polycarbonate glazing samples covered with a hard silicone-based coating (Basecoat Silfort SHP 470 AS4700, Momentive) are passed under an Openair® plasma torch (Plasmatreat) with a rotating nozzle (diameter 22 mm, exit angle 14). °, tilt to the outside) with an output power of 500 volt-amperes.

The plasma torch operates with filtered air at a pressure between 3 and 4 bar. The plasma torch is fixed and the edge of the samples moves in front of the end of the torch at a speed of 2m / minute.

The edge of each sample undergoes a single pass under the plasma torch. The distances between the surface of the glazing and the end of the nozzle are indicated in table 1. The axis of the torch is normal in relation to the plane of the glazing.

After a single passage of the sample under the plasma torch, the surface energy (wettability) of the treated region is measured according to ISO 8296 with an ethanol-based test solution. The values obtained are indicated in table 1.

Next, each of the following primer compositions is applied on the plasma treated region.

IPDI CPO-w: Chlorinated isophorone polyolefin diisocyanate in water (LOCTITE TP661 (Henkel))

CPO-s: Chlorinated polyolefin in a xylene / ethylbenzene mixture (KORATAC GM510 (Kommerling))

CPO-w: Polyolefin chlorinated in water (HARDLEN EW5515 (Toyobo))

IPDI-w: isophorone diisocyanate in water (WITCOBOND 434-27 (Baxenden))

IPDI-s: isophorone diisocyanate in a mixture of n-butyl acetate / ethyl acetate / butanone (SIKA 209IM (Sika)) IPDI-MDI-s: isophorone diisocyanate and 4,4'-diphenylmethane diisocyanate in a mixture of ethyl acetate / butanone (SIKA 209D (Sika))

The application is carried out using a foam impregnated with the primer composition.

The solvent is allowed to evaporate at room temperature, the edge of the glazing samples is introduced into an encapsulation mold and overmold either with a TPE-V (Sarlink® 4775B42, Teknor Apex Co.) or with a plasticized PVC ( APEX® 1523F3, from Teknor Apex Co.).

No preheating of the glazing takes place between the priming stage and the encapsulation. After encapsulation, the samples are stored for 7 days at 23 ° C and 50% relative humidity, then subjected to the following accelerated aging conditions: 14 days at 70 ° C and 95% relative humidity, then two hours at -20 ° C.

The quality of the adhesive contact is evaluated by a 90 ° detachment test (100 mm / min traction speed). The peel strength in N / cm and the percentage of adhesive or cohesive rupture are measured according to ASTM-D413.

Table 1 shows all the results obtained:

Comparative samples without plasma treatment are simply cleaned with isopropanol.

Table 1

It is observed that in samples according to the invention in which the distance between the nozzle and the surface of the hard coating is 2 and 4 mm, all the values of peel strength are greater than 10 mN / m. On the contrary, for samples that have not undergone any plasma treatment or that were subjected to a plasma treatment with a substrate / torch distance of 8 mm, the resistance to peeling is insufficient in most cases.

It is also observed that the resistance to detachment is greater in the samples treated at a distance of 2 mm than for those treated at a distance of 4 mm.

The surface energy of the samples after the plasma treatment is the greater the smaller the nozzle / surface distance.

Claims (8)

A method for encapsulating a polycarbonate glazing comprising, on at least one of its faces, a silicone-based hard anti-abrasion coating, said method comprising the following successive steps: a) treating a region of the face of the glazing that carries the silicone-based hard coating by atmospheric plasma with a plasma nozzle having a power comprised between 100 volt-amperes and 1,000 volt-amperes, the distance between the end of the plasma nozzle being and the surface of the glazing at most equal to 7 mm, b) applying, on said region treated by atmospheric plasma, a primer composition comprising one or more adhesion promoters selected from the diisocyanates, polyisocyanates and chlorinated polyolefins, in solution or suspension in an organic or aqueous solvent, c) evaporate the solvent to form a dry primer layer, and d) overmolding a thermoplastic polymer over the region covered by the dry primer layer. Method according to claim 1, characterized in that the relative speed of movement of the plasma nozzle with respect to the glazing is between 2 and 4 m / minute. Method according to claim 1 or 2, characterized in that the distance between the end of the plasma nozzle and the surface of the glazing is less than 6 mm, preferably at most equal to 5 mm, and in particular between 2 mm and 4 mm. Method according to any one of the preceding claims, characterized in that the plasma nozzle operates with a carrier gas pressure, preferably filtered air, comprised between 3 and 4 bar. Process according to any one of the preceding claims, characterized in that the adhesion promoter (s) are selected from the group consisting of isophorone diisocyanate (IPDI), 4,4'-diphenylmethane diisocyanate (MDI) and chlorinated polyolefin grafted with maleic anhydride. Method according to the preceding claim, characterized in that the primer composition consists essentially of one or more adhesion promoters selected from diisocyanates, polyisocyanates and chlorinated polyolefins, in solution or suspension in an organic or aqueous solvent. Method according to any one of the preceding claims, characterized in that the thermoplastic polymer is chosen from styrenic thermoplastic elastomers (TPE-S), vulcanized olefinic thermoplastic elastomers (TPE-V), poly (vinyl chloride), thermoplastic polyurethanes (TPU), poly (methyl methacrylate) (PMMA), polycarbonates (PC), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), polycarbonate / acrylonitrile-butadiene-styrene blends ( PC / ABS) and polypropylene (PP). Method according to any one of the preceding claims, characterized in that the thermoplastic polymer is an elastomer, preferably an elastomer selected from thermoplastic elastomers and poly (vinyl chloride).